Known devices may be helpful in providing in-vivo imaging. Autonomous in-vivo imaging devices, such as swallowable capsules or other devices may move through a body lumen, imaging as they move along. In an in-vivo imaging device having a certain field of view (FOV) and incorporating a corresponding illumination system, the illumination is achieved by one or more light sources having a certain field of illumination (FOI).
Reference is now made to FIG. 1A, showing a schematic two dimensional presentation of an optical system according to an embodiment of the prior art. Referring to FIG. 1A, optical system generally referenced 100 may be included in, an in-vivo imaging device, but may be included in other suitable devices, such as an endoscope, trocar, or other in-vivo imaging device. Optical system 100 may include, for example, light sources 142 and 143, an imager 146, and one or more optical heads 149 (which may comprise lenses and a lens holder or a lens cover) disposed behind a viewing window such as optical dome 154, for viewing, for example, a target or object 115. One, two, or more than two illumination sources may be used. FOI 142′ (indicated by dots) defines the area illuminated by light source 142, while FOI 143′ (indicated by asterisks) defines the area illuminated by light source 143.
The FOI illuminated by each light source, such as light sources 142 and 143, is typically stretched over a relatively wide area, with a varying intensity of illumination that is proportional to the distance from the light source. A ray of light, for example ray 150, may exit a light source, for example light source 142, and reflect back from the dome 154 through the optical head 149 to the imager 146. Such reflected rays, which are typically viewed as bright white spots in the image, may cause a partial obstruction of the image.
FIG. 1B is an exemplary graphical illustration of the illumination distribution within a FOI, such as FOI 142′ or 143′, of a single light source, for example a commercially available white LED. The illumination distribution within a FOI of a light source is best described as a Gaussian distribution as characterized by the Gaussian curve 180. In cases where four light sources are employed, for example within an optical system of an in-vivo imaging device, four overlapping areas are created between the FOI of each light source. For example, as depicted in FIG. 1C, for each light source 142, 143, 144 and 145 four FOI 142′, 143′, 144′ and 145′ exist, respectively. The partial overlaps between FOI of each light source may create four distinct areas which are strongly illuminated whereas in other areas illumination may be diminished in comparison. For example, as depicted in FIG. 1D, the area created at the conjunction of the four overlapping FOI 142′, 143′, 144′ and 145′ is strongly illuminated, while other areas are more weakly illuminated.
A frequent problem encountered in optical systems for in vivo imaging is that stray light and backscatter may reflect from the optical window of the in vivo device. Such stray light may be received by the receiving means (e.g., an image pickup element) and cause partial obstruction of the image due to the reflections, which are typically viewed as bright white spots in the image.
There is a need for an in vivo device that will provide unvarying, uniform illumination in the in-vivo device field of view, with minimal impediment of stray light reflections.